The problem is money. The expert panel estimates it would cost about $3 billion a year beyond NASA’s current budget.

“Under the budget that was proposed, exploration beyond Earth is not viable,” panel member Edward Crawley, a professor of aeronautics at MIT, told The Associated Press Tuesday.

The panel's report provided options for President Barack Obama but said NASA’s current plans would have to change in any case. Five years ago, then-President George W. Bush proposed returning astronauts to the moon by 2020. To pay for it, he planned on retiring the shuttle next year and shutting down the international space station in 2015.

All those deadlines would have to change, the panel said. Space exploration would work better by including other countries and private for-profit firms, it said, and NASA's budget would have to be increased in order to move forward with "an exploration program that will be a source of pride for the nation."

If America cannot achieve the goals set for space exploration, even after international and commercial partners pitch in, "it should accept the disappointment of setting lesser goals," the report said.

The $3 billion option
Crawley indicated that he didn't favor that option. The extra $3 billion a year would be “unquestionably worth it,” he told AP.

U.S. Sen. Bill Nelson, a Florida Democrat who flew on the space shuttle in 1986, said in a statement that "unless the president is willing to invest an extra $3 billion a year, America will surrender the global leadership in science and technology it derives from space exploration. He needs to act boldly, like President Kennedy did before him."

NASA spokesman Michael Cabbage told The Washington Post that the space agency "will be working with the administration to determine how best to shape the agency's human spaceflight efforts for the future." The White House said it would release the panel's full report once it is received.

The panel, chaired by retired aerospace executive Norman Augustine, includes executives, scientists and former astronauts. The committee telegraphed its conclusions during hearings that were conducted weeks ago, but those conclusions came into sharper focus in a summary report that was posted online Tuesday.

The report said that the space agency appeared to be "on an unsustainable trajectory," pursuing goals that did not match the allocated resources. NASA already has spent $7.7 billion on the moon plan, including the design and construction of new rockets. But recent estimates have claimed that following through on the plan would cost $100 billion to $150 billion over the next decade.

Resources vs. rhetoric
The report could influence the White House agenda for human spaceflight for years to come. Experts inside and outside the government have been looking to the Augustine panel to provide clear guidance on space policy, and the report could provide political cover if Obama decides to scale back the space vision laid out five years ago.

Former NASA associate administrator Alan Stern said the report highlighted the harsh reality that the space agency's vision had “a mismatch between resources and rhetoric.” Now, he said, Obama faces a choice of “essentially abandoning human spaceflight” or paying the extra money.

Signals on whether the White House will downsize NASA's ambitions or bulk up its budget are likely to come during deliberations over the coming fiscal year’s spending plan.

The Augustine panel's summary report covered topics ranging from the fate of the space shuttle fleet to the long-range goals of space exploration:

The panel noted that shuttle operations were likely to stretch into the second quarter of 2011, rather than ending in 2010 as anticipated. One option would provide for an even longer extension of shuttle operations. If that option is chosen, a new independent safety panel should be convened to recertify the shuttle fleet for flight, the panel said.

The panel said it was "concerned" that the international space station may be vulnerable after the shuttle fleet's retirement. Deorbiting the station in 2015 would be "unwise," considering the billions of dollars that were spent constructing the orbital complex, it said. "The committee finds that the return on investment of ISS to both the United States and the international partners would be significantly enhanced by an extension of ISS life to 2020," the report said.

The report lays out several options for developing spaceships to take the shuttle's place, but it notes that NASA's schedule for rolling out a new launch vehicle known as Ares 1 "no longer supports the ISS." The committee suggested establishing "a new competition" in which large and small companies would vie to provide transport services to the space station on a commercial basis. NASA, meanwhile, could move directly to the development of a heavy-lift Ares 5 rocket or an alternate launch system based on shuttle technology. An Ares 1 prototype is due for its first test launch next month, but some observers have wondered whether that test should go forward.

Panel members urged the federal government to stimulate commercial activity in space by awarding guaranteed contracts for orbital services, just as the government supported the airline industry in the 1920s by doling out airmail delivery contracts. That would leave NASA free to focus on developing the technologies and concepts for exploration beyond Earth orbit. "It is time for NASA to reassume its crucial role of developing new technologies for space," the report said.

Although human exploration beyond Earth orbit was not considered viable under current budget guidelines, increasing the budget by $3 billion a year would "produce results in a reasonable timeframe," the panel said. One option for an expanded program would focus on a return to the moon (the so-called "Moon First" option). Another option would start by building up overall capabilities in human spaceflight, and then turn attention to landings on the moon, Mars or other destinations such as near-Earth asteroids and Martian moons (the "Flexible Path" option).

The panel tended to emphasize the Flexible Path option. "There's a lot of places in the neighborhood," Crawley said. "In fact, going to the moon is more difficult than going to a near-Earth object."